American Trypanosomiasis Chagas Disease

Organism Trypanosoma cruzi. The trypano-some in American trypanosomiasis undergoes a development cycle both in the vector bug and the vertebrate host, with trypomastigotes, the infective form and pseudocysts forming in the muscle. These contain amastigotes, which grow a flagellum to become promastigotes and epimastigotes (Fig. 15.18) when the pseudocyst ruptures, finally developing into infective trypomas-tigotes (Fig. 15.19). The trypomastigote of the American disease has a larger kineto-plast and is more curved than the African one. The infection differs in that repeat cycles take place in the host's muscles producing a chronic disease state.

Clinical features American trypanosomiasis presents as an acute infection, generally in children, with fever, local swelling at the site of inoculation and enlargement of the regional lymph nodes. Muscular tissues are attacked so that in adult life, chronic conditions such as enlargement of the heart, oesophagus or colon develop. Heart failure and cardiac irregularities are common manifestations that lead in the course of time to disability and early death. In HIV infection, acute myocarditis or meningoencephalitis can occur.

Diagnosis is by finding the organism in the blood in the acute stage. Methods of concentrating the erythrocytes or xenodiagnosis (feeding of laboratory-reared clean bugs on the patient) are often required. In the chronic case, serological tests may be positive.

Transmission is by Reduviidae bugs, differing from area to area according to the species of the Reduviidae and the reservoirs of infection. The main genera of bugs are Triatoma, Rodnius and Panstrongylus, which can be differentiated from each other by their antennae and mouth parts (Fig. 15.19). Essentially, there are two cycles, one wild and the other domestic, which are illustrated in Fig. 15.20.

In the wild cycle, armadillos, opossum, raccoons and a number of other animals have been found infected, living in close proximity to their burrow-inhabiting bugs. This infection remains as a zoonosis until disturbed by a domestic animal, commonly a dog ferreting around the burrows of these wild animals. They are attacked by the bugs and acquire the infection. On returning to the house, the dog becomes a reservoir for the domestic bugs, which transmit the infection to any humans living or staying in the house.

In Central America, the cycle is semi-domestic with the reservoir maintained in the domestic rat (Rattus rattus), from which house-haunting bugs pass on the infection to people in the house. Although the bugs feed on people, it is the passage of trypanosomes in the bug faeces, which are rubbed into the wound or conjunctiva that produces the infection.

The bugs live in cracks in the walls and floors and within the thatch in the roof. The mud and wattle type of structure is particularly suited to the conditions required. The number of bugs hiding within the cracks and crevices can be several hundreds.

Infection can also be transmitted by blood transfusion, and small epidemics in a group of people sharing the same food suggests that contamination of food by bug faeces could lead to transmission by the oral route.

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